CBSE Class 11 Maths Notes: Sequences & Series – Geometric Progression

A G.P. is a sequence whose first term is non-zero and each of whose succeeding term is r times the preceding term, where r is some fixed non – zero number, known as the common ratio of
the G.P. For example 3 + 9 + 27 + 81 is a G.P. whose common ratio is 3.

nth Term and Sum of n Terms:

If a is the first term and r the common ratio, then G.P. can be written as a, ar, ar2, . . . the nth term, an, is given by an = arn-1. The sum Sn of the first n terms of the G.P. is